Very low flows in the upper Colorado River system are now expected to trigger calls from senior water rights tied to the Shoshone hydropower plant and irrigators in the Grand Valley. And, starting Friday, more water is to be released from Ruedi Reservoir into the lower Fryingpan River to bolster downstream flows.

The Shoshone plant has two water rights, a very senior 1902 right and a less-senior right for 158 cubic feet per second with a 1929 priority date. A call for the 1929 Shoshone right is expected to take effect on Thursday, meaning those upstream from the Shoshone hydro power plant in Glenwood Canyon who hold junior rights must stop diverting.

On July 1, another, larger call is expected to happen downstream on the Colorado — the Cameo call. The Cameo call is made up of the water rights of agriculture diverters near Palisade, including the Grand Valley Water Users Association and the Orchard Mesa Irrigation District.

The Cameo call, which is the second-most senior water right on the Colorado River, calls about 2,200 cfs down through the river system, but the diversion structures tied to the call also have the potential to nearly dry up the Colorado River in a 15-mile reach between the Palisade area and the confluence of the Gunnison River in Grand Junction. This 15-mile reach is critical habitat for endangered fish, including the Humpback Chub.

To help offset the effects of the Cameo call and other diversions on the river system, officials with the Upper Colorado River Endangered Fish Recovery Program have set a low-flow target of 810 cfs this year.

And, after meeting with other regional water managers on Wednesday, officials with the U.S. Fish and Wildlife Service plan to release on Friday 50 cfs of water that has been earmarked specifically for endangered fish from Ruedi Reservoir. Another 100 cfs will be added to the bolstered flows on Monday, bringing releases to about 260 cfs in the river below Ruedi Reservoir.

While a Cameo call is not unusual and often happens in late summer, this is the earliest it has ever taken effect, according to Don Meyer, Senior Water Resources Engineer with the Colorado River District. The previous record was July 14.

“It’s a brutal year,” Meyer said. “I think it’s going to be a dire situation for everybody, but especially the fish down there.”

This year is also the second earliest that “fish water” has been released from Ruedi Reservoir since the endangered fish program was established in 1988. During the most recent drought years, 2002 and 2012, fish water was released on June 24 and July 3, respectively.

Federal officials this year expect to be able to release 16,412.5 acre-feet of fish water from Ruedi Reservoir this year, including from a 5,000 acre-foot pool, a 5,412 acre-foot-pool and 6,000 acre-feet of water owned by Ute Water Conservancy District in the reservoir, which is to be leased for the endangered fish program.

In all, the fish program has a total of 28,000 acre-feet of water it can use from various reservoirs in the upper Colorado River system, including Ruedi, Granby and Wolford reservoirs.

The Cameo call will also put more water into the Roaring Fork River by “calling out” the transmountain diversion through the Twin Lakes tunnel under Independence Pass. The Twin Lakes Reservoir and Canal Company can move 625 cfs of water out of the Roaring Fork Basin to the Arkansas Basin, where it is used for East Slope municipal and irrigation purposes.

The tunnel is currently diverting around 50 cfs, but that will come to a halt when the Cameo call goes into effect.

“In one respect it’s a windfall for the Roaring Fork,” said Kevin Lusk, president of Twin Lakes Reservoir and Canal Company. “It’s not good for our customers, but that’s the law. It’s just part of owning a water right on a river in Colorado. This is one of those dry years so we are not surprised to see the Cameo call come on.”

Editor’s note: Aspen Journalism is covering rivers and water in collaboration with The Aspen Times and Glenwood Springs Post-Independent. More at http://www.aspenjournalism.org.